C# 14: User increment/decrement support.

[michaelnebel]

In this PR we add support for user defined instance decrement/increment operators.

Example:

public class C
{
    public int Value { get; private set; }

    public C(int value)
    {
        Value = value;
    }

    public void operator ++()
    {
        Value++;
    }
}

Similar to user defined compound assignment operators, the increment/decrement operators manipulates the instance they are applied to. This requires changes to the dispatch logic for such operator calls.

[michaelnebel]

DCA looks good

• Performance appears to be un-affected.
• There are some minor changes to the number of extraction errors/missing call targets, but it appears to be due to the wobliness that we sometimes experience (this is at least indicated by the re-runs). Also, I didn't expect any changes here, as the increment/decrement operators were extracted prior to this change - but the name was just incorrect and the dispatch logic was missing.
• There is some alert wobliness as well, but it doesn't appear to be related to the changes in this PR either.

[Copilot]

Pull request overview

Adds C# 14 support for user-defined instance increment/decrement operators (mutating this), updating both extraction and QL-side call/dispatch modeling so these operator calls are represented and dispatched correctly in the C# CodeQL libraries and tests.

Changes:

• Extend C# extractor operator-name handling to correctly render op_*Assignment-style increment/decrement operators without appending =.
• Add QL library support for modeling instance mutator operator calls and include them in dispatch logic alongside other instance-operator-style calls.
• Expand/adjust C# library tests (AST, operator call, and dataflow) to cover instance ++/-- (including checked forms) and extension-operator scenarios.

Show a summary per file

File	Description
csharp/ql/test/library-tests/operators/PrintAst.expected	Updated AST expectation output to include new instance ++/-- operator declarations and call sites.
csharp/ql/test/library-tests/operators/Operators6.ql	New library-test query covering increment/decrement operator targets and calls.
csharp/ql/test/library-tests/operators/Operators6.expected	Expected results for the new operator-target/operator-call test.
csharp/ql/test/library-tests/operators/Operators5.expected	Updated expected locations due to added code shifting line numbers.
csharp/ql/test/library-tests/operators/Operators4.expected	Updated expected location due to added code shifting line numbers.
csharp/ql/test/library-tests/operators/Operators3.expected	Updated expected location due to added code shifting line numbers.
csharp/ql/test/library-tests/operators/operators.cs	Added a class with instance ++/-- operators and call sites (including checked block usage).
csharp/ql/test/library-tests/extension/PrintAst.expected	Updated AST expectations for extension operators, including ++/--.
csharp/ql/test/library-tests/extension/extensionTypes.expected	Updated expected locations due to added extension-operator content shifting line numbers.
csharp/ql/test/library-tests/extension/extensions.expected	Updated expected call/parameter/operator expectations to include ++/-- extension operators and new line numbers.
csharp/ql/test/library-tests/extension/extensions.cs	Added extension operator ++ and operator -- plus call sites to exercise extraction/dispatch.
csharp/ql/test/library-tests/dataflow/operators/operatorFlow.expected	Updated dataflow expectations to include flow through instance mutator operator ++.
csharp/ql/test/library-tests/dataflow/operators/Operator.cs	Added a new test class exercising mutation/dataflow through instance operator ++.
csharp/ql/lib/semmle/code/csharp/exprs/Call.qll	Introduced an InstanceMutatorOperatorCall concept for instance mutator operator invocations.
csharp/ql/lib/semmle/code/csharp/dispatch/Dispatch.qll	Updated dispatch modeling to treat instance operator calls (compound assignment + mutator) consistently.
csharp/ql/lib/semmle/code/csharp/Callable.qll	Updated unary-operator classification to allow parameterless non-static ++/-- operators.
csharp/ql/lib/change-notes/2026-05-12-user-increment-decrement.md	Added change note for the new C# 14 instance ++/-- operator support.
csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/Invocation.cs	Updated invocation target-resolution to use context-aware GetTargetSymbol.
csharp/extractor/Semmle.Extraction.CSharp/Entities/Expression.cs	Refactored target-resolution to be context-driven and reused in call-type detection.
csharp/extractor/Semmle.Extraction.CSharp.Util/SymbolExtensions.cs	Adjusted operator-symbol rendering to avoid incorrectly producing ++=/--= for assignment-suffixed operator method names.

Copilot's findings

• Files reviewed: 20/20 changed files
• Comments generated: 3